Presence of:H2: Squeaky Pop Test: use a lit split to light a small sample of gas in a test tube. If Hydrogen, then a Squeaky pop will occur. O2: Glowing Splint Test: Add a still glowing splint to a small sample of gas in a test tube. If Oxygen, the splint with reignite. CO2: Limewater Test: Bubble the gas through a sample of Calcium Hydroxide, Ca(OH)2 . If Carbon Dioxide, a white precipitate of Calcium Carbonate, CaCO3 will form from the original clear liquid. Cl2: Bleach Test: Place a piece of litmus paper in a sample in a test tube. If Chlorine, the litmus will go from either blue or red to white in colour.